1. Field of the Invention
The present invention relates to a small-sized loudspeaker capable of reproducing a large sound input signal.
2. Description of the Related Art
In recent years, small-sized sound reproduction apparatuses occupying less space have been used. Most loudspeakers used in such sound reproduction apparatuses are small in diameter. A conventional small-sized loudspeaker is provided with a diaphragm having a small diameter. Therefore, the vibration amplitude of the diaphragm is required to be increased in inverse proportion to the area of the diaphragm and to the square of the intensity of the sound signal to be produced in order to obtain a predetermined sound pressure.
A conventional loudspeaker has a structure in which a damper, or a suspension, supporting a diaphragm is generally made of fibers impregnated with resin and has a corrugated cross-section of a number of concentric circles. The damper with such a structure (i.e., the corrugation damper) should be displaced in such a manner that the corrugations of the damper are stretched when the diaphragm is vibrated. In this case, as the amplitude of the diaphragm of the damper becomes larger, the radius of each concentric circle of the damper should be changed (increased) more widely.
In the conventional damper, vertexes of the corrugations are concentrically positioned. Thus, there is no mechanism by which the radius of the corrugations of the damper may increase in accordance with the increase in amplitude of the vibration of the diaphragm. In order to realize a predetermined large amplitude of the diaphragm, the material constituting the damper is required to have sufficient circumferential stretch/shrinkage properties.
However, the fibers impregnated with resin which are typical materials for the damper generally stretch less because of their small elasticity. Thus, sufficient change in radius of the corrugations cannot be obtained. This limits the obtainable magnitude of a feasible amplitude, making it impossible to obtain a sufficiently large amplitude. Therefore, it is difficult in the conventional small-sized loudspeaker to obtain a very large amplitude particularly when a sound signal in a low frequency region is reproduced.
As described above, the conventional small-sized loudspeaker has a structure in which the damper is unlikely to be deformed to such a degree as to allow the diaphragm to vibrate at a large amplitude, which makes it impossible to reproduce a sound signal with a large electric power. In particular, bass reproduction characteristics are poor, increasing the distortion of a reproduced signal.